Compositions and methods for depositing amorphous metal-phosphate coatings on metal surfaces



Patented Feb. 28, 1950 OOMPOSITIONS AND METHODS FOR DEPOS- ITINGAMORPHOUS METAL-PHOSPHATE COATINGS ON METAL SURFACES Harold I.Roaenbloom, Pittsburgh, Pa, alslgnor to Bail Laboratories, lno.

No Drawing. Application November 23. 1945, Serial No. 630,548

24 Claims. (Cl. 117-127) This invention relates to methods or processesof depositing coatings or films on metal surfaces to make them resistantto corrosion by applying chemical solutions to such metal surfaces, andto chemical compositions which may be employed in making up suchchemical treating solutions.

An object of this invention is to provide a process whereby metalsurfaces may be protected against the corrosive action of the atmosphereby wetting the surfaces to be protected with a solution containing awater soluble salt of a. metal and a glassy or amorphous phosphatewhereby an amorphous metal phosphate film or coating is deposited on thetreated surfaces.

Another object of the invention is to provide a process of the characterabove set forth in which the chemical solution employed is operative inan unheated state, is rapid in its coating action, and which does notattack the metal or cause the metal itself to lose weight.

A further object of the invention is to provide a process of thecharacter set forth above in which the treating solutions are capable ofcontrolled replenishment so that they may be maintained in an active andoperative condition, thereby making continuous processing of metalspossible without wasteful use of chemicals.

A still further object of the invention is to provide a chemicalcomposition containing certain chemical compounds so proportioned withrespect to each other that treating baths or solutions suitable for theprocesses may be made up for use by operators unskilled in the chemicalarts. and whereby, through the use of simple tests, the effectiveness ofthe solution may be readily determined and replenishment thereofeffected by the addition of said composition to the solution in amountsindicated by the tests.

And a still further object of the invention is to provide a compositionfor, and a method of. treating metal surfaces to deposit thereoncoatings which not only protect against corrosion, but also formdesirable and useful bases for finish coatings, such as paints,lacquers, enamels, and which improve the bonds between the metals andsuch finish coatings, and in the case of organic coatings, gives themetals a high degree of pro tection against attack in corrosiveatmospheres.

The chemical treatment of metals, particularly ferrous metals which arequite susceptible to corrosion, has been racticed for many years.Oeschger Patent No. 1,354,263 being one of the process forming aprotective coating by chemical reaction of the phosphate with an ironsurface to be coated. Coslett Patent 1.007.069 and Heathcote, BritishPatent 29,504 both teach the use of phosphate solutions with attackferrous metals to provide a corrosion resistant surface. Many subsequentpatents have been issued which pertain to the use of processes involvingthe chemical reaction of the phosphate treating solution and the metalsurface. In all of these processes, there is a visible etching orroughenlng of the metal and a loss of metal weight.

Roland application Serial No. 468,690 filed December 11, 1942, nowabandoned, discloses the treatment of ferrous metals with solutionscontaining certain molecularly dehydrated phosphates and 'a minimumconcentration of p. p. m. of calcium, strontium, barium, zinc, orcadmium. In this process, an amorphous metal phosphate protectivecoating consisting of the reaction product of the molecularly dehydratedphosphate and the metallic element selected is deposited upon the metalsurface, there being no visible attack of the metal by the phosphatetreating solution.

The invention of this application involves improvements over theaforesaid application of Roland.

I have found that adequate protective phosphate coatings may bedeposited on many metals other than the ferrous metals. For example, I

'may treat iron, steel, copper, zinc, silver, magnesium, and many alloysof these several metals. Although unalloyed ferrous metals are usuallyextremely susceptible to atmospheric corrosion. the other metals whichmay be treated by my process are also susceptible to corrosion invarying degrees.

when certain materials which function as oxidizing agents are employedin the coating solutions. a number of new and unexpected results andadvantages are obtained. Notably, the treating solution deposits thedesired amorphous metal phosphate coating without heating of thesolution; the coating is deposited at a rapid rate; the solution may bemade more concentrated by being capable of adjustment to lower pHvalues; the solutions are more stable and do not decompose to anymaterial extent: the solutions may be replenished and restored to theirinitial condition by adding to the working solution the chemicals usedin making up the solution initially in the same proportions as they werepresent in the original solution, and in the amounts required to restorethe solution to its original or desired concentration; the ratio ofcoating metal ion to phosphate does not change materially from that ofthe original solution even though a substantially large percentage ofthe total coatin materials in the original solution have been removedthus making replenishment easy and sub- Ject to control: and lastly, thesolutions are operative at relatively low pH values in the acid rangewithout attacking the metal surfaces being treated.

Heretofore, the deposition of a commercially satisfactory protectiveamorphous metal phosphate coating was considered impracticable if notimpossible at solution temperatures of about 25 C. (room temperature)unless the metal surfaces were in contact with the treating solutionsfor ten minutes or more. I have found that an acceptable coating may bedeposited on metal surfaces in approximately ten seconds at 25 C. byusing my preferred composition in accordance with the process of thisinvention. I have also found that such amorphous metal phosphatecoatings may be applied in less than ten seconds if the solutions aremaintained at slightly elevated temperatures or if relatively highconcentrations of the chemical compositions are used in the solution.Operation of the coating process at room temperature has a two-foldadvantage, a saving in heat and equipment costs and a prolongation ofthe effectiveness of the solutions. By adapting my process to thecontinuous production of sheet metals an amount of the protectivephosphate coating can be applied in such a short period of time that therate of output is not retarded.

In practicing the invention. the metallic surfaces to be coated arefirst cleaned to remove soil. I then apply the treating solution to thecleaned metal surfaces either by immersion of the metal in the treatingsolution or by spraying the solution on the metal. In many cases,spraying the treating solution on the metal is preferred.

While the treating solution is in contact with the metal, an amorphousmetal phosphate iilm is deposited on the surface thereof. The rate atwhich the film is deposited at a given temperature of solution isdependent on a number of factors such as the concentration of and theparticular kind of metal ion and phosphate employed in the solution andthe ratio of the metal ion to phosphate, the pH of the solution and theamount and kind of oxidizing agent employed.

After the metal has been subjected to the treating solution. the excesssolution may, if desired. be removed from the metal surfaces by rinsing.A preferred rinsing step if used is described more in detail elsewhereherein.

The treating solution may be made by adding to a known quantity of waterat least one watersoluble salt of the metals of the group consisting ofcalcium, zinc, magnesium. cobalt. cadmium. iron, aluminum, barium,strontium, manganese, chromium, a molecularly dehydrated phosphate suchas a glassy or amorphous alkali metal phosphate, for example, glassysodium phosphate. an oxidizing agent, and if necessary a pH adjustingchemical which will establish the desired pH in the solution. The metalsalts of the above group may for convenience be called coating metals.

The coating metals and phosphate are added to give a preferred weightratio of metal ion to phosphates and in total amount to provide anoptimum concentration at the pH selected. as set later herein in moredetail.

By the term molecularly dehydrated phosphate glass, I means the glassyphosphates having the 4 ratio formula of xMaOtlPrOs. A practical rangeof ratios of MzOtPnOs extends from about 0.4:1 to about 1.7 :1 where Mis an alkali metal or the ammonium radical. In the examples I havedisclosed a specific sodium phosphate glass. also known commercially assodium meta-phosphate glass or a glass of the metaphosphate type. whichhas a ratio of NaaOiPrOs of about 1.1:1. The glassy phosphates in therange from 0.4:1 to about 1.1:! are more or less acid, from the ratio ofabout 1.1:1 to about 1.7:! the glasses range from about neutral toalkaline. The glass having a ratio of about 1.721 is most alkaline,having a pH in 54% solution of about 9.5 to 9.8. The pH of a 36%solution of a sodium phosphate glass of the ratio of about 0.4:1 isabout 2 or less. The glasses in between these limits have intermediatepH values in solution depending on the particular ratio of NasorPzos andthe extent to which the glass is dehydrated.

The coating or film which deposits on meta surfaces from the treatingsolutions is an amorphous metal phosphate. The composition of thecoating as determined by analysis is that of a metal phosphate. Forexample, the amorphous coating deposited from an aqueous solution madeup from calcium chloride, sodium phosphate glass. and an oxidizingagent, has approximately the composition of CaiPOz): and is amorphous.

The coating metals above mentioned may be in the form of chlorides,nitrates. sulfates, acetates, oxides, carbonates, or hydroxides. Thesulfates and acetates are not as desirable as the chlorides and nitratesbecause the rate at which the amorphous metal phosphate coating isdeposited is not as high as that attained with the chlorides andnitrates of these metals.

In the practice of the invention by industry, it is advantageous that aprepared composition be available from which coating solutions can bemade by merely dissolving specified quantities of the composition inwater in the proportions required for any particular or desiredconcentation of solution. Since the glassy phosphates suitable for thesecompositions are more or less hygroscopic. the coating metal salts, thepH adjusting materials, and the compounds which act as oxidizing agentsshould be relatively anhydrous to avoid caking of the composition duringstorage. The preferred metal salts are therefore chlorides. If thenitrates were readily obtainable in relatively anhydrous form, theywould be more preferable for my purpose than the chlorides.

0f the various water soluble salts which react with the phosphate todeposit the amorphous metal phosphate coating on metal surfaces. calciumchloride is a desirable salt because it is relatively inexpensive.readily available in the market as a dry material, and is an effectivecompound for my purposes.

The water soluble salts which act as oxidizing agents and are suitablefor purposes oi this invention may be in the form of nitrates, nitrites,sulfltes, permanganates, chromates. perborates. and ierricyanides. Ofthese. the sodium and potassium salts are preferable in that they arereadily availabe at reasonable cost. In the practice of my invention Ihave found sodium nitrite. sodium nitrate. sodium suliite. sodiumperborate, potassium permanganate, potassium dichromate. potassiumferricyanide. and sodium hypochlorite, to be both practical andeii'ective. However, any water soluble salt or substance which functionsT as an oxidizing agent may be employed.

In the prior art processes. where the orthophosphate coating solutionsare employed. both oxidizing agents and reducing agents have been usedto accelerate the rate at which coatings are formed. However. in theseprocesses the solutions must be heated to temperatures ranging from160-200 F. In my process, furthermore. the reducing agents are noteffective in that they deter the formation of the phosphate coating andin some cases prevent its formation. The relative eifects of oxidizingagents and reducing agents on my coating solution are shown later hereinby Table 1.

The effectiveness of my compositions and the solutions made therefrom orsolutions made up from the individual components of the compositions,depends on the total concentration in solution of coating metal salt andphosphate glass. the ratio of the coating metal ion to phosphate in thesolution and the oxidizing agent employed. The maximum concentration ofmetal ion and phosphate in the solution at a given temperature dependson the pH of the solution.

By effectiveness of my composition in solutions made from the componentsof the composition. I mean the quality of and the rate at which anamorphous metal phosphate coating will be deposited per unit area ofmetal surface per unit of time. The quality of the coating is a factordeterminable by certain tests, for example, tests which indicate theability of the coating or film to protect the metal against attack when(1) immersed in distilled water for a specified number of hours. (2)exposed to salt spray for a given nuniber of hours, (3) exposed toatmospheric conditions at high or saturated humidities, and other wellknown tests. The ability of the coating to hold a paint or other finishwhen exposed as above. is also a measure of its quality. When metalswhich have been coated with the metal phosphate coatings in accordancewith the invention are painted. and the painted surface is scratchedthrough to the metal. the quality of the coating is measured by itsability to prevent the spread of corrosion beyond the area of thestretch. and by its ability to prevent the paint from lifting of! thesurface of the metal in the area contiguous with the scratch.

I have found that in order to obtain an effective amorphous metalphosphate coating on metal. the solution must contain not less than acertain minimum concentration of metal ion. Where calcium chloride isthe coating metal salt employed. minimum effective concentration ofcalcium ion is about 100 p. p. In. by weight. While the solution to beeffective must contain not less than a certain minimum of calcium ion.the weight ratio of molecularly dehydrated phosphate to metal ion mustbe held between certain limits. the maximum ratio being perhaps morecritical than the minimum from the standpoint of abi ity of the solutionto coat metal surfaces satisfactorily. I have also found that for a iventotal concentration of metal ion and molecularly dehydrated phosphateglass, and a given ratio of such phosphate to metal ion at thatconcentration. the solution will produce optimum coatings at a given pHvalue. In other words. there is an optimum pH value for a given solutionat which optimum coating results are obtained. This is not to say.however. that effective coating results cannot be obtained at other pHvalues because eflective coatings can be so obtained. By varying theconcentration of metal ion and proper adjustment of the pH of thesolution to obtain optimum coating. the weight ratio of phosphate tocalcium may vary between 0.05:! to about 12:1. In this ratio range theoptimum pH values will lie in the range from pHii.0 to pH 8.0. Forsolutions containing 100 p. p. m. of calcium, the effective weight ratioof phosphate to calcium is in the range of about from 2:1 to about 8:1,that is, 200 p. p. m. of phosphate to 100 p. p. m. of calcium to 800 p.p. m. of phosphate to 100 p. p. m. of calcium. As the concentration ofcalcium is increased. the ratio range of phosphate to calcium isbroadened. Thus, in a solution containing 5000 p. p. m. of calcium theeii'ective ratio range of phosphate to calcium lies between values ofabout 0.05:1 and about 12:1.

long as the proper ratio between calcium. or other coating metalemployed, and molecularly dehydrated phosphate is maintained, andprovided the solution is adjusted to the proper pH, there appears to beno real upper limit to the total concentration of metal salts such ascalcium chloride. and molecularly dehydrated phosphate.

I have found that in the coating solutions a very orderly relationshipexists between the following variables: pH value, total concentration ofthe sum of coating metal ion and molecularly dehydrated phosphate. andthe ratio of coating metal ion to molecularly dehydrated phosphate.Thus, for a given time and temperature of treatment, I may preparesatisfactory treating solutions over a wide range of pH, concentration,and ratio of metal ion to phosphate. In order to adjust the pH of mycoating solutions above pH about 5. a buffer must be employed. Forexample. if NaOH alone is used to adjust the pH of the coating solutionfrom an initial pH of 5 to a final pH of 8, the properties of thesolution are such that the pH will slowly return to near the originalvalue. A buffer such as borax in conjunction with NaOH or other suitablealkaline material is satisfactory for adjusting the pH above 5. Nospecial precautions need be observed when adjusting the solutions to pHvalues below about 5. I have found, for example, that at any given pHwithin the range above disclosed. I may prepare relatively moreconcentrated solutions merely by increasing the ratio of phosphate tometal ion. If, on the other hand. I choose to maintain a constant ratioof phosphate to metal ion, I may then prepare concentrated solutions byworking in the lower range of pH values. When I prefer to employsolutions in the higher range of pH values, I may do so by usingrelatively lower total concentrations. keeping the ratio of metal ion tophosphate fixed: or, if I prefer to work both at a relatively highervalue of pH and total concentration I may do so by increasing the ratioof phosphate to metal ion.

I have found that amorphous metal phosphate protective coatings can bedeposited from treating solutions containing a metallic element in thesol tion, an oxidizing agent, and a soluble molecularly dehydratedphosphate over a rather broad range of pH values running from a minimumof 3 to a maximum of about 8. However, I have found that solutionscontaining a mixture of calcium and aluminum as metal ions inconjunction with the molecularly dehydrated phosphate glass in properproportions and an oxidizing agent, will produce satisfactory amorphousphosphate coatings at pH values as low as 2.0. there being no visibleattack on the metal even at this low pH value. When I employ a treatingsolution having a total concentration 01 calcium and moiecularlydehydrated phosphate of about 9000 p. p. m. by weight, the ratio ofcalcium to phosphate being 1:5. the most satisfactory pH range is from 3to 5, whereas when I use a solution containing about 1800 p. p. m. ofthe sum oi calcium and phosphate in the ratio of 1:5, the preferred pHrange is from about 4 to about 8. I have found that at a concentrationoi 5.5% (88,300 p. p. m. of the combined calcium ion and phosphate) at apH value 3, a protective amorphous metal phosphate coating is veryrapidly deposited on a ferrous metal surface. The pH value of thesesolutions may be controlled by adding the proper amount of eitheralkaline or acidic compound to the solutions or to the preparedcompositions; or I may use a combination of metallic compounds andcertain molecularly dehydrated phosphates which will produce the desiredpH value without Iurther adjustment.

1 have prepared numerous compositions which may be dissolved in water toform effective treating solutions which may be used in accordance withthis invention. By way or illustration, the following compositions aregiven which have proved to be very satisfactory for commercial use.

Sumcient amount of pH adjusting agent added to bring pH value to about4.0 when this omnposition is dissolved in water to give a concentrationof approximately 2%.

Chemical Components complgdmm 0 oi. as?) n 1 a 000mm?) aao floldgummetaphosphate glass (ratio of NaaOzPaOw a 2 Sumcient amount of pHadjusting agent is added to bring pH value to about 4.5 when thiscomposition is dissolved in water to give a concentration ofapproximately 1.75%. In this example two coating metal salts (calciumchloride and cobalt chloride) are employed.

Chemical Components Percent Zn(NO ):.3H;0 61. 1 killing: metaphospbstsglass (ratio of NuOzlhOw 88. a

Bumcient amount oi pH adjusting agent is added to bring the pH value toabout 5.0 when this composition is dissolved in water to give aconcentration oi approximately 1.5%. an example of a compound in whichthe metal ion and oxidizing agent (N03) are supplied by one compound.

Chemical Components compnqnmon CdCh Pamga 5 soldium motsphosphate glass(ratio of Nag0:P,O|- sustains::::::::::.1.i111:1:1::;:::::: 11:31:11:323

Suflicient amount of pH adjusting agent is added to bring the pH valueto about 4.5 when this composition is dissolved in water to provide aconcentration of about 1.9%.

Chemical Components cmpasmnn P Mn(NO|)a.6H10 T B. 0

metaphosphate glass (ratio 0! Macaw.-NBN'OI::::::::::::::::::::IIIII::::::::::::::: 21

Suiiicient amount of pH adjusting agent is added to bring the pH valueor the solution to about 4.0 when this composition is dissolved in waterto provide a concentration oi about 1.9%.

Chemical Components compsmon Percent BrCig 43. 7 Bofiufn metaphosphataglass (ratio of NEQOZPgQs 55.5 NIQCHOLRHIO 0. B

Suflicient amount of pH adjusting agent is added to bring the pH valueto about 3.7 when this composition is dissolved in water to provide aconcentration or about 1.5%.

Suficient amount of pH adjusting agent is added to bring the pH value ofa solution of this composition to about 2.5 when the composition isdissolved in water to provide a concentration of about 2%.

Chemical Components g Percent OoCh 45.0 OdCiJMEO.....- 24.5 Holdingmctophosphats glass (ratio of N801P20i= 0 30. NlsUhOy 0. 5

Bumcient amount of pH adjusting agent is added to bring the pH value ofthe solution to 15 about 4.5 when this composition is dissolved inThisis.

water to provide a concentration of about 2.5%. where the compositionsabove described are made up as a dry mixture and sold as such to be usedfor making coating solutions by adding the same to water in amountsrequired to give the desired concentration, the pH adjusting material,preferably in anhydrous form, isadded to the mixture. Thus, in each ofcompositions A and B, I have included sodium acid sulfate in suchamounts that when a solution of 1.4% by weight concentration is made up.the pH of the solution will be about 3.8. When preparing solutions ofcompositions A and 13 having either a greater or lesser concentrationthan 1.4%. the pH of the solution is automatically adjusted to theapproximate optimum level. Thus, if I prepare more concentratedsolutions, the concentration of sodium acid sulfate is likewise greaterand the solution has a relatively lower pH. For example a /2% solutionof composition A or B will have a pH of about 3.2. Conversely, asolution more dilute than 1.4%, having a lesser amount of sodium acidsulfate, has a relatively higher pH. For example, the pH of a /4%solution. of composition B is 4.5. The concentration of oxidizing agentis likewise automatically present in these solutions in approximatelythe optimum amounts, because the amount is always proportional to theconcentration of the solution.

If it is desired to make up coating solutions from the individualcomponents of the composition above stated, a liquid rather than a solidacidifying or pH adjusting material may be employed. Thus, for example,instead of solid sodium acid sulfate, I may employ hydrochloric acid toadjust the solutions to the desired pH value.

I have found that a 1.4% solution of composition A containing sodiumacid sulfate as the pH adjusting agent has a coating rate of about 36men/sq. ft./min. at room temperature, whereas a similar solutionadjusted to the same pH with hydrochloric acid instead of sodium acidsulfate has a coating rate of 64 mg./sq. ft./mln. at room temperature.The rate of coating of composition B containing sodium acid sulfate asthe pH adjusting agent, is about 62 mg./sq. ft./min. Since it has beenobserved that almost 70% of the coating deposited in one minute isformed during the first seconds of contact with the treating solutionboth compositions A and B are satisfactory for commercial applicationeven though the sodium acid sulfate interferes to a certain extent withmaximum deposition of the amorphous calcium phosphate film. I mayovercome the slight inhibiting eflect of the sulfate. however, byresorting to the use of another type of solid acidifying agent such asaluminum chloride, for example, if I desire to obtain maximum coatingweight.

In practical applications, solutions prepared from compositions A or B,produce relatively uniform coatings during a treatment of a large areaof metal surface and thus require only infrequent replenishment in orderto maintain the solutions at uniform effective coating efllciency. Ihave found, for example, that when the time of contact between 1.4%solution of composition B and metal is one minute, the solution being atroom temperature (about 25 C.) approximately 800 sq. ft. of metal perpound of composition may be effectivel coated without making additionsto the solutions. The weight of coating obtained during this period willnot vary by more than :20% of the average coating weight value of 50mg./sq. it. If I use a like concentration of 10 composition A under thesame conditions I may treat approximately 800 sq. ft. of metal surfaceper pound of composition without making additions to the solution. Inthis instance, the coating weight will not vary by more than :15% of theaverage value of 38 man/sq. It. I have found that in treating metalswhich are to be subsequently finished with an organic coating such as apaint or lacquer, a very short immersion time of the order of 5 to 60seconds is adequate. For example, in the case of 2.5% solutions preparedfrom compositions A or B, the coating rate at room temperature is sorapid that a treating time of 5 seconds produces adequate coatings.

In composition A, 6.6% by weight of sodium nitrite is present. Whencomposition A is dissolved in water to concentration of 1.4%, the amountof sodium nitrite present in the solution will be approximately 0.09% byweight. In composition B, 0.'l% of sodium dichromate ls present. whenthis composition is dissolved in water to a concentration of 1.4% byweight, there will be approximately 0.01% of sodium dichromate presentin the solution. On a weight basis, sodium dichromate is considerablymore effective for my purposes than sodium nitrite, consequently smalleramounts are required in the dry compositions.

As has been pointed out, one of the advantages of my compositions whendissolved is that the composition ratio of coating metal ion tophosphate remains substantially fixed even after long periods of use andthe metal ion-phosphate concentration is depleted to the extent of about35%. When depleted to this extent the solution should be restored to itsoriginal condition by merely adding the required amount of thecomposition and adding suilicient water to compensate for loss ascarry-out or spray loss. In this respect the invention is a substantialimprovement over the aforementioned Roland application.

In a typical treating solution such as is formed by preparing a 1.4%solution of composition B, the ratio of calcium to sodium metaphosphateglass is approximately 1:5. This ratio remains substantially constant upto a point where the concentration of the solution has been depleted toabout 30-35%. In the course of reaching this point of depletion, theratio will vary in narrow limits from 1:5 to about 1:4.74, but beyondthis point the ratio decreases rapidly. Therefore, the proper time toadd replacement material is beiore this point is reached. To determinethis, the concentration of one of the components of the solution isdetermined. I may take samples of the solution and analyze for P205content by any well known method, for example a colorimetric phosphatetest, or I may analyze the sample for calcium content by one of severalmethods. I prefer to determine P205 concentration since this may be donequite rapidly with reasonable accuracy, whereas the determination ofcalcium is either less rapid, or less accurate, depending upon themethod chosen. Having determined that the treating solution has reacheda point requiring additional materials, I merely add the ready-mixedcomposition in sufficient amounts to restore the bath to its originalconcentration.

Although my new compositions and the various solutions I have developedwill produce a corrosion resistant coating on many metal surfaces whichwill adequately protect the surfaces for reasonable periods of time ifthey are exposed ll to atmospheric conditions, the primary applicationof my compositions and processes is in theileldofprocessingmetalswhicharetobesubsequently coated with organicfinishes or vitreous enamels Whenametalsuchashotorcoldrolledsteeliscleanedanddriedandanorganicflnishis applied. the slightest break inthe protective illm will enable corrosion to set in thereby causingoxidimtion not only at the exact point of rupture but in the surroundingarea as well. It is common knowledge that when the paint cover ing asteel surface is so scratched that the steel is exposed, corrosion willoccur rapidly at the scratch and will soon cause a lilting of the paintfrom the surface adjacent the scratch. Eventually the corrosion extendsfrom the scratch to a large surrounding area.

Light gauge steel sheet or strip which is painted or lithographed isfrequently formed into various shapes in a later operation and in theseforming operations quite frequently the protective coating is rupturedthereby enabling corrosion to set in. When the metal is treated in theusual orthophosphate type solution. the coating formed is crystalline,and consequently cannot withstand sharp bending to the degree toleratedby the amorphous phosphate coatings which are deposited from thesolutions of my invention.

Since the solutions I employ do not visibly attack a metal surface butdeposit a transparent glass-like film, the advantages are obvious if thesurface is to be covered by a transparent varnish or lacquer. Not onlyis the surface protected against corrosion and the lacquer firmly boundto the amorphous phosphate, but the surface of the metal is visiblyunimpaired. This means a great deal when decorative metals, possessing anatural lustre or a pleasing surface design are treated with mysolutions and subsequently lacquered or varnished. The ordinaryorthophosphate treatment would visibly etch the metal so that itsdesired appearance would be obliterated. The reflective power of metalstreated by my process is affected but slightly whereas it is destroyedto a very large extent by the mat iinish of the orthophosphate coating.

The amorphous phosphate coatings are pertectly smooth as contrasted withthe uneven surface of the orthophosphate coatings and less 50 paint orvarnish is required to cover a given area of metal protected by mycoatings than an equivalent area protected by the crystalline coatings.

As was mentioned previously, oxidizing agents have desirable andunexpected effects in the treating solutions made up from compositionsused in accordance with this invention, whereas reducing agents eitherreduce materialy the effectiveness of the solutions or in some casesnullify their efl'ectiveness. The following table shows the relativeeffects of oxidizing and reduclng agents on coating solutions of thisinvention.

Table 1 Effect of oxidizing and reducing agents in treating solutionscontaining 1500 p. p. m. by wshht of calcium (from calcium chloride) and7500 p. p. m. by weight of sodium phosphate glass-ratio otNaaO:P:Ot=l.l:l.

Temperature of solution 40 0.; pH 3.5; time of immersion of cold rolledsteel panels, minutes. Weight of phosphate coating expressed inmilligrams per square decimeter and per m 100.

Goncentra- Weight oi Phosphate tldn Gusting Percent by Oridiaing: WMMJdsl. ism/q. fl.

None ll.8d=l.6 l1l:i;l5.0 NaNOa 0. 06 30. 5 285 0. 10 32. 3 an 0. 30 31.9 as it 3% 3'5 misc. 01 on 2011 m 2-2.: a: Nanci 0111 1111 m0 0. 34 22.0 212 til 3%? KMno. gal 1% 10a 4 7 35% i2 13;

KsFuCN). 0. 10 30. 5 342 NBO l 3 182 gr 178 one 11.8:bl. 6 llltlll 0Hydmquiuone g g: "Elon" 0101 a o 75 (p-mcthylamlnophenol) 0. 10 l. 0 0.4 Such 0.01 0. 7 63 0. l0 5. 8 H

In the following Table II, the client of oxidizing agent on a coatingsolution at 25 C. is shown. The solution as made contained 7500 p. p. m.of sodium phosphate glass having a ratio of NazOiPsOs of about 1.1:1,3000 p. p. m. oi calcium from calcium chloride, 2.46 grams of NaHBO; toadjust the pH of the solution to 3.8. The solution was divided into twoequal parts. To the one, no oxidizing agent was added, to the other, 100p. p. m. of NazCrz-Ow was added as oxidizing agent. A steel test panelwas placed in each solution for one minute and the coating weightdetermined.

The solution containing p. p. m. of NBsCl'zOr gave a coating weight overthree times heavier than the solution without any NaaCnO-a in one minuteof contact with the solution.

I have found that if the treated metal is given a specially adjustedchromic acid rinse immediately after exposure to the coating solution,superior bond is obtained between an organic coating and the treatedmetal surface. If

chromic acid itself is used, the results are not noticeably superior tothose obtained when specimens are rinsed in plain water. but I haveicund that by adiusting the pH of the chromic acid rinse solution,extraordinary results are obtained. For example, chromic acid solutionin a concentration of 0.05% has a pH of about 2.3, but if I adjust thepH of this solution so that its pH value is in the range of from about3.9 to about 10 6.5, the adherence of the paint to the metal surface ismarkedly improved as is the salt spray resistance and the ability towithstand water immersion test. The optimum pH range I have found forthe 0.05% chromic acid rinse solution 15 is from about 3.0 to about 5.4.The rinse step may 13 be performed by immersing or rinsing the coatedsteel in the adjusted chromic acid solution for about one minute orless, the temperature of the solution being in the range of from about40 C. to about 100 C. although I have found that superior results areobtained at the lower temperatures in this range.

A 0.1% solution of chromic acid has a pH of about 2.0 but if I adjustthe pH value to within the range of from about 3 to about 5.5, theoptimum range being about 3.5 to about 5.5, I again observe startlingresults in the adherence corrosion and water immersion resistance of thesubsequently applied organic coatings. Although the use of a plain waterrinse following the deposition of the phosphate coating on metallicsurfaces produces satisfactory results, I prefer to employ the adjustedchromic acid rinse since there is a definite improvement over the use ofwater. I may also use dichromates or chromates, provided the pH of thesolutions of these is adjusted to or falls within the range abovestated. The metal undergoing treatment may be taken from the phosphatetreating solution into the dilute adjusted chromic acid bath without anintermediate rinse in water or without an intermediate drying process.Following the chromic acid rinse the metal surface may be dried.

I have found that my metal phosphate coating solution may be applied tometallic surfaces by any means which brings the solution in contact withthe surface, such as by immersion, by spraying, by brushing. or byroller coating. Tests have been conducted in a 4-tank spray washing andtreating unit combined with a drying tunnel. In the first tank, analkaline detergent maintained at a concentration of 1-oz./gallon at atemperature of about 140 F. (60 C.) was used. In the second tank, a hotwater rinse was employed, the temperature of this rinse being in a rangeof 120 F. to 150 F. (49 to 66 C.) with the water being constantlyreplaced through a float controlled valve. In the third tank, a 1%concentration of my composition hereinbefore designated as composition13 was employed at a temperature of about 90 F. (32 C.). Fresh water wasadded only to maintain working volume since there is a certain amount ofcarryover as the metal surfaces moves from this solution to the nextstage in the process. The final operation was a hot water rinsemaintained at a temperature of 120 F. to about 150 F. (49 C.66 C.).

In the first two tanks the metal containers being processed were treatedfor about 40-50 seconds and in the last two stages, contact wasmaintained for about 20 seconds. The finished parts had a multi-colorediridescent sheen which is typical of the amorphous metal phosphatecoating deposited on ferrous metals, and they were free from rustdespite the fact that some moisture remained inside these containerparts as the result of incomplete drying. The corrosion resistance ofthe subsequently painted containers as indicated by the standard saltspray test was excellent.

I have successfully treated large quantities of what is commerciallyknown as bright annealed black plate by spraying the metal with a 1.5%solution of composition B. In this particular processing, the unitconsisted of a series of rubber rolls which moved the metal sheets alongin a horizontal plane between top and bottom spray nozzles. The contacteriod between metal and treating solution was approximately 10 secondsfollowed by a hot water rinse for about 2 seconds and a forced hot airdrying stage. The temperature of the phosphate coating solution wasmaintained in the range of from about -85 F. (24 (L-29.5 0.). Thecoating weight of the phosphate film as determined by the anodicstripping of the coating from small panels in a 10% caustic sodasolution varied from an average of about 31 milligrams per sq. foot atthe beginning of the run to about 30 milligrams per sq. foot at the endof the run.

A large quantity of steel sheets treated by the above mentioned methodwas stored in the mill atmosphere for observation on corrosionresistance in comparison with, similar sheets treated in anorthophosphate bath which produced a crystalline phosphate coating. Theamorphous metal-phosphate coating gave protection superior to bothuntreated sheets and to those which had been run through a treatingprocess using orthophosphate baths.

A portion of the treated sheets was used in the formation of can ends.An observation of the phosphate coating by means of a binocularmicroscope showed the amorphous coating to be perfectly continuous evenover sharp bends, whereas some of the can ends which were treated inorthophosphate solutions showed a rupture of the crystalline phosphatefilm at some points. Samples of both the amorphous metal-phosphatecoated sheets and the crystalline phosphate coated sheets were given anorganic finish by a roller coating process and the can ends were thenstamped from the coated sheets and subjected to an adherence test, ahumidity test, and an outdoor exposure test. Definite superiority in theamorphous metal-phosphate coated can ends was observed in each of thesetests which would indicate that the flexibility of the amorphous coatinghas a definite relationship to the results obtained when coated metalsurfaces are subjected to bending operations.

1 have also employed my treating solution in conjunction with ironsurfaces to be later coated with vitreous enamels. The adherence ofvitreous enamel to the metal surfaces is of prime importance to theindustry and one of the principal obstacles in the one-coat lightenameling process suitable for refrigerators and other similarappliances. is the lack of adherence of the white enamel after it isfired. I have processed iron panels by a standard commercial cleaningand pickling procedure followed by the immersion of these panels indifferent phosphate treating solutions. I have found that the use ofwater-soluble nickel salts in conjunction with a molecularly dehydratedphosphate and the use of water-soluble cobalt salts in conjunction withthe same type of phosphate improves the bond between the vitreous enameland the iron surface. Visual comparison of the degrees of adherence ismade by employing a V inch steel ball loosely held over the enamelsurface and centered over a 1-inch hole in an anvil. The impact of afalling weight on the ball will cause the enamel to separate from themetal if the adherence is not satisfactory, whereas with good adherencequalities, the separation is very slight or almost negligible.

I have found that the amorphous protective phosphate coatings are alsoeflective in the preuse:

vention of high temperature oxidation of metals. For example, a steelstrip coated with a phosphate him when exposed to a temperature of 600C. for one hour will oxidize very slightly whereas an untreated strip isoxidized appreciably. Weight loss measurements indicate that oxidationis reduced appreciably, the reduction being of the order of 90% underthe conditions described.

Having thus described the invention, what I claim as new and desire tosecure by Letters Patent is:

I claim:

1. A water-soluble composition, solutions of which are capable ofrapidly depositing coatings on surfaces of metals to prevent theircorrosion, said composition containing approximately 54.6% by weight ofa sodium phosphate glass having a ratio of NazozPzos of about 1.1:1,about 38.6% by weight of 78% calcium chloride, 6.1% by weight of sodiumacid sulfate and about 0.7% by weight of sodium dichromate, saidcomposition being characterized by the fact that a protective amorphouscalcium phosphate coating is deposited in approximately ten seconds froma solution containing approximately 2.5% by weight of said compositionat a solution temperature of approximately 25 C.

2. A process for depositing an amorphous metalphosphate coating on thesurfaces of metals to prevent corrosion thereof which comprisessubjecting a metallic surface composed of at least one of the metals ofthe group consisting of iron, copper, zinc, silver, and magnesium to theaction of an aqueous solution having a pH value between about 3 and 8,and containing in solution at least 100 p. p. m. by weight of a metalion of at least one element selected from the group consisting ofcalcium, zinc, cobalt, magnesium, cadmium, iron, aluminum, barium,strontium, manganese, chromium, and nickel, at least 200 p. p. m. byweight of a water-soluble alkali-metal phosphate glass and at least 10p. p. m. of an oxidizing agent selected from the group consisting ofwater-soluble inorganic nitrates, nitrites, suliltes, permanganates,chromates, ferricyanides, dichromates, and perborates, and maintainingthe ratio of the phosphate glass concentration in said solution to theconcentration of the metal ion therein between the values of about0.05:1 and about 12:1.

3. A process for depositing an amorphous metal-phosphate coating onmetal surfaces to prevent the corrosion thereof which comprisessubjecting a metallic surface composed of at least one of the metals ofthe group consisting of iron, copper, zinc, silver, and magnesium, tothe action of an aqueous solution having a pH value between 2.0 and andcontaining in solution at least 100 p. p. m. by weight of the ions ofcalcium and aluminum, at least 200 p. p. m. by'

weight of a water-soluble alkali-metal phosphate glass and at least p.p. m. of an oxidizing agent selected from the group consisting ofwater-soluble inorganic nitrates, nitrites, sulfides, permanganates.chromates, ferricyanides, dichromates, and perborates.

4. The method as defined in claim 2 in which the alkali-metal phosphateglass has a molar ratio of alkali-metal oxide to P205 of from about,0.4:1 to about 1.7:1.

5. A process for depositing an amorphous metal-phosphate coating onmetal surfaces to prevent corrosion thereof which comprises subjecting ametallic surface composed of at least one of the metals of the groupconsisting of iron, copper, zinc, silver, and magnesium, to an aqueoussolution having a pH value between 3 and 8, and containing from about p.p. m. to about 10,000 p. p. m. by weight of a metal ion of at least oneelement selected from the group consisting of calcium, zinc, cobalt,magnesium, cadmium, manganese, chromium, iron, aluminum, barium,strontium, and nickel, at least 200 p. p. m. by weight of awater-soluble alkali-metal phosphate glass and at least 10 p. p. m. ofan oxidizing agent selected from the group consisting of water-solubleinorganic nitrates, nitrites, suliltes, permanganates, ferricyanides,chromates, dichromates, and perborates.

6. A process for depositing an amorphous metal-phosphate coating onmetal surfaces to prevent the corrosion of metals which comprisessubJecting a metallic surface composed of at least one of the metals ofthe group consisting of iron, copper, zinc, silver, and magnesium, to anaqueous solution having a pH value of from about 3 to about 8 andcontaining not less than about 100 p. p. m. of a metal ion of at leastone element selected from the group consisting of calcium, strontium,chromium, manganese, barium, zinc, cadmium, cobalt, nickel, magnesium,alumlum, and iron, a water-soluble alkali-metal phosphate glass, and notless than about 10 p. p. m. of an oxidizing agent selected from thegroup consisting of water-soluble inorganic nitrates, nitrites,sulfltes, permanganates, ferricyanides, chromates, dichromates, andperborates for accelerating the rate of deposition by said solution ofan adherent protective amorphous phosphate fllm on said metal surface,and maintaining a ratio between the concentration of the phosphate glassand the metal ion in the solution between the values of about 0.05:1 andabout 12:1.

'1. A process for depositing an amorphous metal-phosphate coating onmetal surfaces to protect the same against corrosion which comprisessubjecting a metallic surface composed of at least one of the metals ofthe group consisting of iron, copper, zinc. silver, and magnesium to theaction of an aqueous solution having a pH value in the range of fromabout 3 to about 8 and containing from about 100 p. p. m. to about10,000 p. p. m. by weight of a metal ion of at least one elementselected from the group consisting of Ca, Zn, Co, Mg, Cd, Fe, Al, Ba,Sr, Cr, Mn, and Ni, a water-soluble alkali-metal phosphate glass inamount to give a weight ratio of said phosphate glass to the element ofsaid group between about 0.05:1 and 12:1 and at least 10 p. p. m. of anoxidizing agent selected from the group consisting of water-solubleinorganic nitrates, nitrites, sulfides, permanganates, ferricyanides,chromates, dichromates, and perborates.

8. A process for depositing an amorphous metal-phosphate coating onmetal surfaces to protect the same against corrosion which comprisessubjecting a metallic surface composed of at least one of the metals ofthe group consisting of iron, copper, zinc, silver, and magnesium, tothe action of an aqueous solution containing at least 100 p. p. m. of ametal ion of at least one element selected from the group consisting ofCa, Zn, Co. Mg, Cd, Fe, Al, Ba, Cr, Sr, Mn, and Ni, and also containinga water-soluble alkali-metal phosphate glass in amount to give a weightratio n of said phosphate glass to the element of said our: betweenabout 2:1 and about 12:1 and at least p. p. m. or an oxidizing agentselected from the group consisting of water-soluble inorganic nitrates,nitrites. sulfites, permanganates, ferricyanides, chromates,dichromates, and perborates, the pH value of said solution being betweenabout 3 and 8.

9. A process for depositing an amorphous metal-phosphate coating onmetal surfaces to protect the same against corrosion which comprisessubjecting a metallic surface composed of at least one of the metals ofthe group consisting of iron, copper, zinc, silver, and magnesium to theaction of an aqueous solution containing at least 100 p. p. m. of ametal ion of at least one element selected from the group consisting ofCa. Zn, Co. Mg, Cd, Fe, Al, Ba, Sr, Cr, Mn, and Ni, and containing analkali-metal phosphate glass in which the molar ratio of alkali-metaloxide to P20 is from 0.4:1 to about 1.7:1, the amount oi glass in saidsolution being such as to give a weight ratio of said glass to saidmetal ion of between about 0.05:1 to about 8:1, and the concentration ofphosphate glass being not less than about 200 p. p. m. by weight, thetreating solution also con taining at least 10 p. p. m. by weight of anoxidizing agent selected from the group consisting of water-solubleinorganic nitrates. nitrites, sulfltcs. permanganates. ferricyanides,chromates, dichromates, and perborates, the pH value of the solutionbeing adjusted to a value between about 3 and about 8.

10. A process for treating metal surfaces composed of at least one ofthe metals of the group consisting of iron, silver, magnesium, copper,and zinc to withstand corrosion which comprises subjecting a metal ofsaid group to an aqueous solution containing at least 10 p. p. m. byweight of an oxidizing agent selected from the group consisting ofwater-soluble inorganic nitrates, nitrites, sulfltes, permanganates,chromates, dichrornates, ferricyahides, and perborates, a metal ion ofat least one element selected from the group consisting of calcium,zinc, cobalt, magnesium, cadmium, iron, aluminum, barium, strontium,manganese, chromium, and nickel, and a watersoluble alkali-metalphosphate glass, the combined amount of said metal ion and saidphosphate in the solution being from about 300 p. p. m. by weight toabout 50,000 D. p. m. by weight and the ratio of alkali-metal phosphateglass to said metal ion being within the range or about 0.05:1 and about12:1 so that an amorphous phosphate of said metal ion will deposit as afilm upon the metal being treated, said film being suflicient to protectthe metal from corrosion, the pH value oi the solution being maintainedat a value between about 3 and 8.

11. A method of rapidly forming a protective amorphous metal-phosphatecoating on metal surfaces composed oi at least one of the metals of thegroup consisting of silver, magnesium, copper, iron, and zinc whichcomprises treating said metals with an aqueous solution having a pHvalue of from 3 to 8, and at a temperature range of about 15 C. and notin excess of about 50 C., said solution containing a metal ion 01' atleast one element selected from the group consisting of calcium, zinc,cobalt, magnesium, cadmium, iron, aluminum. barium, strontium,manganese, chromium and nickel, at least 10 p. p. m. by weight of anoxidizing agent selected from the group consisting of water-solubleinorganic nitrates, nltrites. aulfltes, permanganates, terricyanidcs.

chromates, dichromates, and perborates and at least 200 p. p. m. of awater-soluble alkali-metal phosphate glass, the concentration of themetal ion being not less than p. p. m. and the ratio of phosphate glassto metal ion in said solution being such that there is deposited uponthe metal being treated an amorphous metal-phosphate protective coatingexceeding one milligram per square decimeter in approximately tenseconds.

12. A method whereby metal surfaces composed of at least one metal ofthe group consisting of iron, silver, magnesium, copper, and zinc, maybe treated to resist corrosion which comprises contacting a metal ofsaid group for a relatively short period of time with a non-heatedaqueous solution containing in solution at least 10 p. p. m. by weightof an oxidizing agent selected from the group consisting ofwater-soluble inorganic nitrates, nitrites, sulfltes, permanganates,chr0- mates, dichromates, ierncyanides, and perborates, at least 200 p.p. m. of a water-soluble alkalimetal phosphate glass and a metal ion ofat least one element of the group consisting of Ca, Zn. Co, Mg, Cd. Fe,Al, Ba, Sr, Mn, Cr, and Ni, the concentration by weight of such metalion being maintained at such a value that the ratio of phosphate glassby weight to metal ion is within a range of not less than about 0.05:1and not more than about 8: l.

13. In the treatment of the surfaces of metals composed of at least oneof the metals of the group consisting of iron, zinc, copper, magnesiumand silver, to produce a protective amorphous phosphate coatingdeposited by contacting the surfaces of such metals with an aqueoussolution containing at least 100 p. p. m. of a metal ion of at least oneelement selected from the group consisting of calcium, zinc, cobalt,magnesium, cadmium, iron, aluminum, barium, strontium, manganese,chromium, and nickel, at least 1U p. p. m. or an oxidizing agentselected from the group consisting of inorganic water-soluble nitrates,nitrites, sulfites, permanganates, ferricyanides, cnromates,dicnromates, and perborates, and at least 2.10 p. p. m. oi awater-soluble alkali-metal phosphate glass, that step which comprisesrinsing said metal surface while wet with the amorphous metal coatingsolution with an aqueous solution of a salt of cnromic acid having aconcentration or Cruz 01' irom about u.0o% to 0.5% and amusted to a pl-ioi irom about 3 to about 5.5.

14. A process as oenned in claim 13 characterized by the fact that themuse solution is a cnromic acid solution having a concentration of Erosor irom about 0.05% to about 0.5% and animated to a pii value or Iromabout is to about 5.5.

15. An aqueous solution for depositing an amorphous metal-phosphatecoating on the surfaces of metals composed of at least one 01 the metalsoi the group consisting of iron, zinc, copper, silver and magnesium,which solution contains as the malor portion of its active chemicalcomposition at least 100 p. p. m. or a metal ion of at least one elementselected Irom the group consisting of calcium, zinc, cobalt, magnesium.cadmium, iron, aluminum, barium, strontium, chromium, manganese, andnickel, and at least 200 p. p. m. of a water-soluble alkali-metalphosphate glass and at least 10 p. p. m. of an oxidizing agent selectedfrom the group consisting of water-soluble inorganic nitrates, nitrites.sulfites, permanganates, chromates, ferricyanides, dichromates, andperborates. the ratio of 19 phosphate to metal ion in said solutionsbeing within the range of about 2:1 to :1.

16. A water-soluble composition adapted for the preparation of solutionsfor forming amorphous metal phosphate coatings on metals at roomtemperature to prevent the corrosion of said metals, said compositioncontaining approximately 49.2% by weight of a sodium phosphate glasshaving a ratio of NasOlPzOs of about 1.1:1, 34.7% by weight of about 18%calcium chloride, about 6.6% by weight of sodium nitrite and about 9.5%by weight of sodium acid sulfate.

1'1. A dry. homogeneous composition which when dissolved in water willform a solution which is etlective to deposit rapidly an amorphousprotective coating on metal surfaces wetted by said solution so thatsaid surfaces are protected by said him against corrosion. saidcomposition containing approximately 49.2% by weight of a sodiumphosphate glass having a ratio of NaaOzPzO: of about 1.1:1, 34.7% byweight of 78% calcium chloride, 6.6% by weight of sodium nitrite and9.5% by weight or sodium acid sulfate, solutions containing about 2.5%by weight of said composition being such that a protective amorphousphosphate coating having a weight of about 44 milligrams per square iootis deposited on the metal surfaces in approximateLv ten seconds ofcontact with said solution at a temperature of about 24 C.

18. A dry, homogeneous water-soluble composition consisting essentiallyof an alkali-metal phosphate glass having a ratio of M20150; of about0.4:1 to about 1.1:]. where M is an alkali metal or the ammoniumradical, a water-soluble compound containing a metal selected from thegroup consisting of calcium. zinc, cobalt, magnesium, cadmium. iron,aluminum, barium, strontium, manganese, chromium and nickel, anoxidizing agent selected from the group consisting oi water-solubleinorganic nitrates, nitrites. sulfltes, permanganates. chromates,ierricyanides, dichromates, and perborates, and a weter-soluble pHadjusting agent, the ratio by weight of the phosphate glass to the metalof the metal-containing compound being between about 0.05:1 and 12:1 sothat when metals of the group consisting of silver, magnesium, copper,iron, and zinc are contacted with a solution containing about 2.5% byweight of said composition, said 2.5% solution containing not less thanp. p. in. of oxidizing agent and not less than 300 p. p. m. of phosphateglass. an amorphous phosphate coating will be deposited on the surfaceof said metals which is eifective to protect the coated surface andprovide a base for paints and enamels.

ill. A composition whose water solutions are capable of depositing onmetal surfaces in contact therewith an amorphous metal-phosphatecoating. said composition consisting essentially of the followingcomponents:

(a) at least one water-soluble salt of a coating metal selected from thegroup consisting of go, Zn. 00, Mg. Cd, Fe, Al, Ba, Sr, Mn, Cr. and

(b) an alkali-metal phosphate glass,

(0) an oxidizing agent selected from the group consisting ofwater-soluble inorganic nitrates, nitrites. suliltes, permanganates.chromates. ferricyanides, dichromates, and perborates,

(d) a dry solid water-soluble pH adjusting comthe proportions ofcomponents (a) and (to being such that when said composition isdissolved in water, the ratio or (bi to the metal ion of (a) in saidsolution is within the ratio range of 0.05: 1 to 12:1, the amount of id)issuch as will produce a pH value within the range oi about 3 to 8, theamount of (c) is such as to give a concentration of at least about 10 p.p. m. by weight, and the amount 01 id) is such as will produce aconcentration of metal ion in said solution or not less than about p. p.m. by weight.

20. A composition according to claim 19 characterized by the fact thatcomponent (a) is a water-soluble calcium salt.

21. A process for depositing an amorphous metal-phosphate coating onmetal surfaces to protect the same against corrosion which comprisessubjecting a metallic suriace composed of at least one metal of thegroup consisting of iron. copper. zinc, silver and magnesium to theaction of an aqueous solution having a pH value in the range or fromabout 3 to 8 and containing at least 100 p. p. m. by weight of a metalion of at least one element selected from the group consisting of Ca,Zn, 00, Mg, Cd, Fe. A1, Ba, Sr, Cr. Mn. and Ni, a. water-solublealkali-metal phosphate glass in amount to give a weight ratio of saidphosphate glass to the metal ion of the element or said group betweenabout 0.05:1 and 12:1 and at least 10 p. p. m. of an oxidizing agentselected irom the group consisting of watersoluble inorganic nitrates,nltrites, ferricyanides, sulhtes, permanganates. chromates. dichromatesand perborates.

22. A process for depositing an amorphous metal-phosphate coating onmetal surfaces to prevent the corrosion thereof which comprisessubjecting a metallic surface composed of at least one of the metals ofthe group consisting of iron, copper, zinc, silver, and magnesium, tothe action oi an aqueous solution having a pli value between about 3 andabout 8 and containing in solution not less than 100 p. p. m. of theions of calcium and a water-soluble molecularly dehydrated alkali-metalphosphate having'a ratio of alkali-metal oxide to PsOs of about 0.421 to1.721, the ratio of the concentration of alkali-metal phosphate tocalcium ion being from about 2:1 to about 8:1, and at least 10 p. p. m.of an oxidining agent selected from the group consisting ofwater-soluble inorganic nitrates, nitrites, sulfltes, ferricyanldes.permanganates, chromates, dichromates. and perborates.

23. A process for depositing an amorphous metal-phosphate coating onmetal surfaces to prevent the corrosion thereof which comprisessubjecting a metallic surface composed of at least one of the metals ofthe group consisting of iron. copper, zinc, silver, and magnesium, tothe action or an aqueous solution having a pH value between about 2.0and about 5.0 and containing in solution not less than 100 p. p. m. ofcalcium ion and also a water-soluble molecularly dehydrated alkali-metalphosphate having a ratio of alkalimetal oxide to Pros of about 0.4:1 to1.7:1, the ratio between the concentration of phosphate and of calciumion being within the range of 0.05:1 and 12:1, and at least 10 p. p. m.of an oxidizing agent selected from the group consisting ofwater-soluble inorganic nitrates. nltrltes, ierrlcyanldes. sulfltes,permanganates, chromates. dichromates. and perborates.

21. A process for depositing an amorphous metal-phosphate coating onmetal surfaces to prevent the corrosion thereof which comprises 21subjecting a metallic surface composed of at least one 01 the metals ofthe group consisting of iron, copper, zinc, silver. and magnesium, tothe action of an aqueous solution having a pH value between about 3 andabout 8 and containing in solution a concentration of not less than 100p. p. m. of calcium ion and a water-soluble molecularly dehydratedalkali-metal phosphate having a ratio of alkali-metal oxide to P205 offrom about 0.4:1 to 1.7:1, the ratio of alkali-metal phosphate tocalcium ion being within the range of about 2:1 to about 8:1, and atleast 10 p. p. m. of sodium dichromate.

HAROLD I. ROSENBLOOM.

22 REFERENCES CITED The following references are of record in the fileof this patent:

UNITED STATES PATENTS Number Name Date 1,254,263 Oeschger Jan. 22, 19182,161,319 Schamberger June 6, 1939 2,337,856 Rice Dec. 28, 1942 102,380,738 Efiier July 31, 1945 FOREIGN PATENTS Number Country Date29,504 Great Britain 1910 475,889 Great Britain 1937

2. A PROCESS FOR DEPOSITING AN AMORPHOUS METAL - PHOSPHATE COATING ONTHE SURFACES OF METALS TO PREVEWNT CORROSION THEREOF WHICH COMPRISESSUBJECTING A METALLIC SURFACE COMPOSED OF AT LEAST ONE OF THE METALS OFTHE GROUP CONSISING OF IRON, COPPER, ZINC, SILVER, AND MAGNESIUM TO THEACTION OF AN AQUEOUS SOLUTION HAVING A PH VALUE BETWEEN ABOUT 3 AND 8,AND CONTAINING IN SOLUTION AT LEAST 100 P. P. M. BY WEIGHT OF A METALION OF AT LEAST ONE ELEMENT SELECTED FROM THE GROUP CONSISTING OFCALCIUM, ZINC, COBALT, MAGNESIUM, CADMIUM, IRON, ALUMINUM, BARIUM,STRONTIUM, MANGANESE, CHROMIUM, AND NICKEL, AT LEAST 200 P. P. M. BYWEIGHT OF A WATER-SOLUBLE ALKALI-METAL PHOSPHATE GLASS AND AT LEAST 10P. P. M. OF AN OXIDIZING AGENT SELECTED FROM THE GROUP CONSISTING OFWATER-SOLUBLE INORGANIC NITRATES, NITRITES, SULFITES, PERMANGANATES,CHROMATES, FERRICYANIDES, DICHROMATES, AND PERBORATES, AND MAINTAININGTHE RATIO OF THE PHOSPHATE GLASS CONCENTRATION IN SAID SOLUTION TO THECONCENTRATION OF THE METAL ION THEREIN BETWEEN THE VALUES OF ABOUT0.05:1 AND ABOUT 12:1.